A basic problem in the Havel river basin is the low water quality (due to eutrophic processes in particular), which could hardly be improved so far in spite of the shut down of various industrial facilities and the modernization of waste water purification. Therefore, the main focus of research will be the analysis and modelling of water quality issues and the assessement of corresponding management options. This aims corresponds directly with the goals of the European Water Framework Directive (EWFD), according to which a ‘good condition’ of open water bodies has to be established within 15 years (§ 4.1). Following § 2 of the EWFD, a surface water body is characterized by a ‘good condition’ in case it can be regarded as good at least from the ecological and chemical point of view. This means that the ‘good condition’ of the EWFD exceeds the ‘good ecological condition’.
Regarding the Havel project, a classification of the Havel river is possible only as long as a chemical classification is performed, based on measured values (appendix VIII und IX EWFD), the recommendations of the LAWA commission (LAWA 1998) and the proposal of Irmer (1999). The latter transforms the German 7-step classification system into the 5-step system of the EWFD.
The research focus ‚Water quality in the Havel river basis and possible improvements by a changed management‘ can be separated into the following sub-foci:
(A) Input of nutrients
The input of nutrients into rivers is induced by geogeneous and antropogeneous depositions as well as by transport processes, which are determined by discharge and natural conditions. Different hydrolgical mechanisms of discharge generation have to be distinguished, covering both near-suface processes (e.g. due to high intensity rainfall events) and sub-surface processes or retention mechanisms of the landscape. Other aspects are the water holding capacity of soils, groundwater table depths and the drainage of agricultural areas. Quantitative aspects of the regional water balance influence directly processes of nutrient input. Here, both diffuse sources (mainly due to agricultural practices) and point sources (mainly input from purification plants and sewage from urbanized areas) must be distinguished.
In spite of various measures concerning water protection in the past, the actual biological water quality of many Havel sections is still ‚critical‘ to ‚strongly polluted‘. One important reason for the slow regeneration of the strongly eutrophic state (especially of the Potsdam Havel) are the still existing high nutreient concentrations of the Berlin urban area entering the Havel and the influence of the over-saturated sediments. Additional loads result from the various inputs of the Fläming region and the rivers Dosse, Jäglitz und Rhin. Since the Spree basin is not a primary part of the study region, results from the GLOWA-Elbe project will be used as input.
(B) Discharge dynamics
Especially in dry summers discharge and flow velocities drop considerably in the lower Havel river. Due to insufficient dilution and sediment solution, the low discharge induces a strong increase in nutrients and a corresponding increase in alga growth. Therefore, studies of water quantity aspects during summer and the induced reduction in water quality are primary research goals. Since the discharge dynamics of the river courses directly influences nutrient transport and remobilization of nutrients from river sediments, the following aspects are of special interest: Hydraulic characteristics of rivers, transformation of selected river sections towards a more natural state, influence of regulative hydrologic measures and water transport between different rivers or sub-basins.
(C) Discharge characteristics of lakes and processes of nutrient remobilization
The Havel river basin is characterized by a large number of lakes and comparable river sections. Questions of dicharge dynamics as well as exchange and ongoing remobilization processes with sediments are, therefore, of high importance for the water quality and for possible management measures.
(D) Interaction between basin area and water bodies
In order to approch the goals of the EWFD, water and nutrient transport processes have to be studied both in rivers and lakes and in the total basin area (combined concept including immission and emission). The basin-wide results must be derived both from point-like studies (field measurements) and from distributed and regionalization methods, including sattelite data.
The feedback mechanisms between the basin area and the water bodies (rivers and lakes) determine considerably the input paths of nutrients from the basin area into the river course by the hydraulic connections of surface and groundwater on one hand and of rivers and lakes on the other hand. Therefore, the nutrient load in rivers is considerably influenced by exchange processes between wetland areas and the lower Havel. The amount of distributed (areal) nutrient output strongly depends on mean- to longterm changes of the agricultural landuse, which on the other hand is strongly determined by regional development plans and the European policy.
(E) Water management
To improve water quality the following approaches of river basin management can be distinguished:
This short overview on the actual situation shows that there is a high need for a modern river basin management in the Havel river basin. Due to the complexity and variability of the various factors influencing water and nutrient balances combined with the distinguished interesses and goals, a scientifically sound approach is necessary. Dince the conflicts mentioned above and others still to come may be influenced by possible climate changes in the future, such additional aspects should be taken into account as well in preparing advices to local and regional stakeholders.
Layout: W. Lahmer